The system in which color images are formed using a subtractive color method where reactions occur between color developing agents and dye forming couplers which form the colors yellow, magenta and cyan, is widely used in silver halide color photographic photosensitive materials.
In recent years, there has been a large amount of research associated with improving dye forming couplers, particularly improving color reproduction and image fastness in silver halide color photographic photosensitive materials. Unfortunately, color developing agents are still limited as an adequate improvement has yet to be realized.
Pyrazolone-based or pyrazoloazole-based couplers have been used conventionally as magenta couplers, but the dyes formed from these couplers sometimes have a poor cut-off on the short wavelength side. Furthermore, synthesis of these couplers involves a complicated, multi-stage routine. They cannot be prepared using a short synthetic technique.
Phenol-based couplers and naphthol-based couplers have been used conventionally as cyan couplers, but dyes produced from these couplers have unwanted absorptions in the blue and green region. They present a major obstacle to the improvement of color reproduction.
Recently, research has been actively pursued into cyan dye forming couplers with novel skeletal structures including nitrogen containing heterocyclic rings, and various nitrogen containing heterocyclic compounds have been suggested. For example, diphenylimidazole-based couplers have been disclosed in JP-A-63-226653, and pyrazoloazole-based couplers have been disclosed, for example, in JP-A-63-199352, JP-A-63-250649, JP-A-63-250650, JP-A-64-554, JP-A-64-555, JP-A-1-105250 and JP-A-1-105251. (The term "JP-A" used herein signifies an "unexamined published Japanese patent application".) These couplers all provide improved color reproduction, and they are characterized by excellent absorption characteristics of the dyes which are formed.
However, the dyes which are produced by the above-mentioned couplers sometimes have an absorption wavelength which is biased to the short wavelength side. In addition, they have poor light and heat fastness. Even another serious problem is that the couplers exhibit a low coupling activity in practice.
Accordingly, these problems need to be effectively addressed, not only for photographic dye forming couplers, but for dye forming couplers as well.